Xe-100
About
The Xe-100 is a small HTGR that produces 80 MWe per module. It uses helium coolant and HALEU TRISO fuel in a pebble-bed core. It is designed for modular multiunit electricity generation and high-heat applications, such as hydrogen production and industrial refining.
| Developer | X-Energy |
|---|---|
| Country of Origin | United States |
| Size | Small |
| Type | High-Temperature Gas-Cooled Reactor (HTGR) |
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Analysis
3
Deployment Timescale
Score Justification
The U.S. NRC is currently reviewing the application for a four-module Xe-100 plant. The Xe-100 benefits from HTGR family precedent. Nuclear-grade systems and a constrained HALEU TRISO fuel supply chain continue to extend deployment timelines.
By indicator
- 2/4 Regulatory Engagement
To what extent has the reactor developer engaged with a recognized nuclear regulatory authority in the licensing process? (30% of total score) - 3/6 Technology Precedent
Has the reactor design, or a sufficiently similar design, been certified anywhere in the world? (10% of total score) - 2/3 Modularity
What share of total reactor systems can be manufactured off-site in controlled factory environments rather than constructed on-site? (15% of total score) - 3/4 Specialization
To what extent do construction activities and components require lengthy qualification processes? (15% of total score) - 2/5 Supply Chain
How mature and available are suppliers for key reactor components and fuel services? (30% of total score)
4
Overnight Cost
Score Justification
The Xe-100’s overnight component costs benefit from a road-shippable modular design and supplier contracts that suggest major nuclear steam supply systems are not giga-scale expenditures per unit. Specialized components required by high-pressure helium coolant conditions may add to these costs.
By indicator
- 3/4 Component Cost
What is the expected cost of the reactor’s major components? (40% of total score) - 4/6 Construction Cost
To what extent does the design reduce construction cost and risk through modular fabrication and limited nuclear-grade specialization? (60% of total score)
3
Operational Cost
Score Justification
The Xe-100’s operational costs are driven by relatively expensive HALEU TRISO fuel and added waste management associated with the extra waste stream from the graphite moderator. While future fuel costs are are highly uncertain, potential savings exist with nth-of-a-kind deployment.
By indicator
- 1/3 Fuel Cost
What is the estimated cost of nuclear fuel per unit of electricity generated, including enrichment, fabrication, and back-end costs? (15% of total score) - 3/4 Maintenance Cost
What is the expected annual maintenance cost for the reactor and balance of plant systems, including consumables? (25% of total score) - 4/5 Staffing Level
How many full-time personnel are required to safely operate and maintain the reactor unit? (40% of total score) - 3/5 Spent Fuel & Radioactive Waste Management Cost
What are the expected operational costs associated with managing spent fuel, including interim storage, transport, disposal, or recycling? (10% of total score) - 5/5 Decommissioning Cost
What are the total lifetime contributions required for decommissioning, regardless of funding mechanism? (10% of total score)
2
Cost Predictability
Score Justification
Cost predictability for the Xe-100 remains limited because a full prototype has not yet been built, although a demonstration reactor is planned in Texas. The design’s modularity is likely to contribute to more consistent manufacturing costs than extensive on-site civil works, once a baseline has been established.
By indicator
- 0/5 Prototype
To what extent has the reactor design been built, demonstrated, or commercially deployed in practice? (75% of total score) - 2/3 Modularity
What share of total reactor systems can be manufactured off-site in controlled factory environments rather than constructed on-site? (25% of total score)
5
Security
Score Justification
The Xe-100 uses HALEU fuel, and its thermal spectrum is not optimized to produce weapons-usable material. X-Energy has worked with the IAEA to incorporate safeguards by design into the Xe-100. Although different from security by design, several overlapping features will benefit the reactor’s security profile, such as the incorporation of unattended monitoring.
By indicator
- 2/3 Fuel
What is the enrichment level and composition of the reactor fuel? (40% of total score) - 4/4 Nuclear Material Production
What is the potential for the reactor to produce weapons-usable nuclear material? (40% of total score) - 1/1 Security by Design
Has the reactor developer built in security by design? (20% of total score)
4
Safety
Score Justification
The Xe-100’s Safety performance is anchored in robust TRISO fuel that retains fission products at high temperatures and an inert, single-phase helium coolant. The design emphasizes long-duration passive decay heat removal. Pressure boundaries rely on multiple functional barriers and confinement rather than traditional containment because the design does not operate at very high pressure.
By indicator
- 1/2 Safety Case
How mature and publicly established is the reactor’s safety case with the regulator? (40% of total score) - 1/2 Shutdown Mechanism
How diverse, independent, and passive are the reactor’s shutdown systems? (20% of total score) - 1/1 Fuel With Safety Characteristics
Does the reactor use fuel with accident tolerance or inherent safety characteristics? (10% of total score) - 2/4 Pressure & Containment
How well does the reactor’s containment strategy protect from the release of radioactive material? (10% of total score) - 3/3 Passive Heat Removal
How long can the reactor remove core heat without operator intervention? (10% of total score) - 4/4 Coolant Reactivity
How chemically reactive is the reactor coolant? (10% of total score)
3
Spent Fuel & Radioactive Waste Management
Score Justification
There is no licensed disposal precedent for TRISO fuel, though qualification efforts are well underway. The Xe-100 produces a relatively large amount of spent fuel volume per unit of electricity because of the multilayered structure of TRISO fuel; however, it exhibits lower decay heat on a volumetric basis because it has much less heavy metal density. This low decay heat is relevant because a geologic repository is largely driven by heat-load, rather than volumetric constraints.
By indicator
- 0/1 Spent Fuel Licensing Precedent
Has the spent fuel form been previously licensed for disposal? (20% of total score) - 3/4 Waste Streams
How many distinct waste streams require separate conditioning or handling pathways? (20% of total score) - 2/3 On-Site Storage
How much on-site area is required for interim spent fuel storage? (10% of total score) - 1/3 Spent Fuel Volume
What volume of spent fuel is produced per unit of electricity generated? (15% of total score) - 2/2 Decay Heat
What is the decay heat output of spent fuel at the 50-year interim storage milestone? (20% of total score) - 2/2 Time to Interim Storage
What is the average time until spent fuel can be transferred to interim storage? (15% of total score)
2
Supply Chain
Score Justification
The Xe-100 relies on specialized components, including helium circulators and nuclear-grade graphite, which currently have limited qualified suppliers. Fuel supply requires HALEU enrichment and TRISO fabrication, which are both currently limited in supply. However, X‑Energy has made progress by breaking ground on its new TRISO Fabrication Facility.
By indicator
- 1/2 Key Component Availability
To what extent are commercial or pilot-scale suppliers available for the reactor’s major components? (60% of total score) - 2/4 Fuel Availability
Are suppliers available for both fuel fabrication and enrichment required by the reactor design? (40% of total score)